TRIANGLES

The most intriguing of three simultaneously published ``Playshapes'' board books (the others are Circles and Squares), this tall right triangle (with slightly rounded corners for safety and durability) opens to form an isosceles triangle that becomes the shape of a tree, the inside of a tent, a mountain, a sailboat, and a party hat. The illustrations, enlivened with busy children, incorporate other triangular forms—e.g., the door formed by lifting the tent flap, the sky it frames, the camper's pack, and the face of her dog. The unpretentious art is bright and cheerful; the format provides tactile reinforcement for a useful concept. An especially good buy for home or classroom. (Picture book. 0-6)